A photovoltaic cell is one of the cleanest and environment-friendly non-conventional energy sources. A photovoltaic cell directly converts solar energy into electrical energy. The electrical energy produced by the photovoltaic cell can be extracted over time and used in the form of electric power. This electric power can be used to drive electric devices. Typically, the power is extracted by use of DC-DC up/down converter circuitry and/or DC/AC inverter circuitry.
The popularity of photovoltaic energy generation is rapidly increasing worldwide. One reason for such popularity is that the energy produced by photovoltaic energy generation is essentially pollution free, unlike conventional energy sources, such as fossil fuel burning thermal power plants, nuclear reactors, and hydroelectric plants, which all raise environmental issues. However, there are difficulties encountered with photovoltaic energy generation that are not present in conventional energy generation systems. These issues include the peculiar current-voltage (IV) droop characteristics of photovoltaic cells, the cost, and the relatively low energy density (efficiency) of photovoltaic cells.
The peculiar IV droop characteristics of photovoltaic cell arrays cause the output power to change nonlinearly with the current drawn from photovoltaic cells. While there may be different types of photovoltaic cells (such as amorphous, crystalline, and other types of photovoltaic cells), all types of photovoltaic arrays show nonlinear power-voltage curves. Furthermore, beyond the fact that the power-voltage curves are different for different types of photovoltaic arrays, the power-voltage curve changes for different radiation levels and temperatures of operation for any given photovoltaic array. Other factors may also contribute to the differences in the power-voltage curves for different types of photovoltaic arrays, as well as to the differences in the power-voltage curve for any given photovoltaic array under different operating or installation conditions.
The near optimal point at which to operate photovoltaic arrays is at or near the region of the power-voltage curves where power is greatest. This point is denominated as the Maximum Power Point (MPP). Photovoltaic cells are still relatively expensive and have relatively low energy densities, and so a wide area is required to generate sizable power. Hence, it is important to operate the photovoltaic cells around the MPP to optimize efficiency.
Techniques exist to at least estimate the MPP for any given photovoltaic array. However, such determination of the MPP is generally performed by a manufacturer (and/or by different agencies or organizations) under certain carefully controlled conditions of temperature, light density, incident angle of the light on the photovoltaic array, wind speed, and other factors that can influence the MPP. Moreover, complicated sensors or other equipment may be needed by the manufacturer to determine the MPP.
Installers, in comparison, do not have the luxury of controlled conditions and complicated equipment when installing a photovoltaic array into a system, and for determining whether the photovoltaic array has been installed or is operating properly near the MPP. The installer generally needs to rely on the MPP data provided by the manufacturer in order to estimate the MPP, and then to tune the system to operate the photovoltaic array near the MPP. This, of course, can lead to inefficient operation of the photovoltaic array, since the environmental (or climatic) conditions, installation conditions, and other actual conditions observed by the installer can change from one point in time to another and since the manufacturer's data generally does not provide the MPP for all possible variations and permutations in such conditions.